This invention relates to an electrophotographic recording material comprising an electrically conductive support; an optional insulating interlayer; a photoconductive layer comprising at least one charge carrier generating compound and at least one charge transporting compound; and a protective transparent covering layer.
In the electrophotographic process described in U.S. Pat. No. 2,297,691 which is now widely used for preparing electrophotographic copies, thorough cleaning of the photoconductor layer is always required after the toner image developed by a dry method on the photoconductor layer has been transferred to the support of the copy. Usually, cleaning is effected by brushing or wiping the layer with suitable brushes or cloths. In copying machines which utilize fluid developers, the effect of mechanical cleaning is frequently enhanced by also using cleaning fluid. In addition to these cleaning operations, the photoconductive layer is also exposed to other influences which may damage it. For example, it is subject to the action of the dry developer and of the developer station (counter-voltage) and during fluid development, additionally to the action of the developer fluid. It is also exposed to ionized air generated in the charging station. It is known that the requisite cleaning procedures and other influences mentioned result in deterioration of the photoconductor layer, or even in mechanical damage thereto, and thus reduce the service life of the photoconductor.
Recording materials comprising a photoconductive layer comprising at least one layer comprising a charge carrier generating compound and a charge transporting compound are known. For example, German Auslegeschrift 2,314,051 discloses use of highly sensitive, organic photoconductor layers on conductive support films or support bands because of their high elasticity.
In particular, very highly sensitive photoconductor systems, such as those disclosed in German Offenlegungsschrift 2,734,288, can be used in the form of endless bands which, because of their high flexibility, can be passed over guide rollers of relatively small diameter.
Patents such as U.S. Pat. No. 2,901,348, U.S. Pat. No. 4,148,637 and German Offenlegungsschrift 2,452,623 disclose protecting photoconductor layers with an additional covering layer of inorganic or organic materials. A disadvantage of such systems is that they are used either on less flexible layers which are composed of or contain selenium, or on generally less sensitive organic photoconductor systems. Moreover, silane couplers, such as chlorosilane, must be added to these covering layers to improve their stability, or the covering layers additionally contain a photoconductive organic compound.